Age, sex and weight matched groups of genetically normal, prediabetic and diabetic Pima Indians and normal Caucasians were examined by means of oral and intravenous glucose tolerance tests, arginine infusions and circulatory mononuclear cell receptor assays, measurement of thickness of muscle capillary basement membrane and urinary protein profiles to determine whether abnormalities of insulin, glucagon secretion or other measurements are characteristic of the prediabetic and diabetic state. BIBLIOGRAPHIC REFERENCES: Aronoff, S.L., Bennett, P.H., Rushforth, N.B., Miller, M., and Unger, R.H.: Normal glucagon response to arginine infusion in prediabetic Pima Indians. J. Clin. Endocrinol. Metab. 43:279-286, 1976. Aronoff, S.L., Bennett, P.H., Rushforth, N.B., Miller, M., and Unger, R.H.: Arginine stimulated hyperglucagonemia in diabetic Pima Indians. Diabetes 25:404-407, 1976.